Shadow mask having conductive layer in poor thermal contact with mask

ABSTRACT

A cathode ray tube for displaying coloured pictures of the shadow mask type. In order to reduce the detrimental increase in temperature of the shadow mask, the shadow mask is provided with a layer which absorbs the incident electrons but is in a poor thermal contact with the shadow mask itself.

United States Patent [191 Bathelt et a1.

[ June 3, 1975 1 SHADOW MASK HAVING CONDUCTIVE LAYER IN POOR THERMAL CONTACT WITH MASK [75] Inventors: Robert Richard Bathelt; Roelof Egbert Schuil, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: July 3, 1974 [2]] Appl. N0.: 485,370

[30] Foreign Application Priority Data July 26, 1973 Netherlands 7310372 [52] US. Cl 313/402; 313/348 [51] Int. Cl HOlj 29/06; HOlj 29/08 [58] Field of Search 313/402, 407, 408, 403,

[56] References Cited UNITED STATES PATENTS 2,886,730 5/1959 Sheldon 313/402 2,971,117 2/1961 Law 313/408 X Primary Examiner-Robert Segal Attorney, A gent, or Firm F rank R. Trifari; George B. Berka [5 7 ABSTRACT A cathode ray tube for displaying coloured pictures of the shadow mask type. In order to reduce the detrimental increase in temperature of the shadow mask, the shadow mask is provided with a layer which absorbs the incident electrons but is in a poor thermal contact with the shadow mask itself.

5 Claims, 3 Drawing Figures SHADOW MASK HAVING CONDUCTIVE LAYER IN POOR THERMAL CONTACT WITH MASK The invention relates to a cathode ray tube for displaying coloured pictures comprising, in an evacuated envelope, means for generating a number of electron beams, 21 display screen comprising a large number of regions luminescing in different colours, and a colour selection electrode having a plurality of apertures, said electron beams being each assigned to luminescent regions of one colour by means of the colour selection electrode, which colour selection electrode is provided with a layer for reducing the temperature of the colour selection electrode.

Such a cathode ray tube is known from US. Pat. No. 2,8 26,538 describing that, in order to promote the radiation of heat, the shadow mask (the colour selection electrode) may be provided with a black layer consisting e.g., of graphite. In such a tube the heat is, indeed, generated in the shadow mask, but the temperature thereof is decreased due to it being a good thermal radiator.

An object of the invention is to attain a still lower operational temperatture of the shadow mask. Another object of the invention is to attain smaller temperature differences in the shadow mask.

According to the invention a cathode ray tube of the kind mentioned in the first paragraph is characterized in that, on the side facing the means for generating the electron beams, the colour selection electrode is provided with an electrically conducting, electronabsorbing layer whose thermal contact with the colour selection electrode is minimal.

In the tube according to the invention the greater part of the electrons incident on the shadow mask is absorbed in a layer which is so thin and whose mechanical contact with the shadow mask is so weak that it cannot cause deformation of the shadow mask. The thermal contact of this layer with the remainder of the shadow mask is so poor that the thermal energy evolved in the layer is not transported in the shadow mask and, consequently, does not affect the deformation of the shadow mask. The electron-absorbing layer preferably consists of a thin metal layer, for example aluminium, secured to the colour selection electrode only along the edges of the apertures. Between said layer and the colour selection electrode may be sandwiched a porous layer, consisting of individual granules The electronabsorbing layer preferably radiates thermal energy well on the side facing the means for generating the electron beams and radiates thermal energy poorly on the other side. For this purpose the layer is preferably a double layer consisting of an aluminium layer provided with a layer of graphite, nickel oxide or nickel iron on the side facing the means for generating the electron beams.

The invention is explained in further detail with reference to the accompanying drawing, wherein FIG. 1 is a longitudinal section of a cathode ray tube for displaying coloured pictures according to the invention:

FIG. 2 is a section ofa part of the shadow mask of the tube shown in FIG. 1', and

FIG. 3 is a section of a part of the shadow mask in accordance with another embodiment of the invention.

The tube shown in FIG. 1 comprises, in a glass envelope l, means 2 for generating three electron beams 3, 4 and 5, a display screen 6, comprising a large number of phosphor regions luminescing in red, blue and green when struck by the electron beams 3, 4 and 5, respectively, and a shadow mask 7 (colour selection electrode), having a large number of apertures 8. Display screen 7 is scanned with the electron beams 3, 4 and 5 under the influence of a set of deflection coils 9. The tube is constructed conventionally in such a way that electron beam 3 strikes only phosphor regions with red luminescence and the beams 4 and 5 only phosphor regions with blue and green luminescence, respectively. It is known that this imposes exacting requirements on the accuracy of the relative positions of shadow mask 7 and display screen 6. Deformation of shadow mask 7 as a result of change in temperature is an important cause of colour defects in the displayed picture. In this connection it should be observed that approximately of the electron beams 3, 4 and S is intercepted by shadow mask 7, which causes considerable generation of thermal energy in shadow mask 7. It is known that the influence of the deformation of shadow mask 7 as a whole may be substantially counterbalanced by means of bimetallic springs, not shown, with which shadow mask 7 is secured in envelope 1. However, the influence of the shadow mask deformation resulting from temperature differences between centre and edge of the shadow mask cannot be counterbalanced. Nor can the influence of local deformation originating from local generation of thermal energy in shadow mask 7 as a result of a very bright portion in the displayed picture surrounded by dark image portions, be compensated for with bimetallic springs.

However, the latter deformations may be reduced by decreasing the evolution of thermal energy in the shadow mask proper. Therefore, according to the invention the thermal energy is evolved in a layer which cannot affect the deformation of shadow mask 7 and whose thermal contact with the shadow mask is inconsiderable. This is elucidated with reference to FIG. 2.

FIG. 2 shows a section of part of shadow mask 7. Some of the apertures 8 are shown in the drawing. A porous layer 10 consisting of individual granules is deposited on shadow mask 7 on the side facing electron gun 2. Layer 10 consists, for example, of manganese oxide (MnO which is sprayed as a suspension and subsequently dried. An aluminium layer 12 is vapourdeposited on layer 10 by means of a process as known, for example, for aluminizing display screen 6. For this purpose layer 10 is covered with an organic skin removable by thermal treatment and consisting e.g., of an acrylic resin. The skin also covers the apertures 8, which are subsequently blown through by means of air. Subsequently an aluminium layer 12 having a thickness of approximately 0.5 pm, is vapour-deposited. Layer 12 contacts iron shadow mask 7 only around the apertures 8. Layer 10 permits bonding layer 12 to shadow mask 7, but has a very low coefficient of thermal conductivity. Consequently, the thermal energy evolved in layer 12 is removed substantially by radiation. To prevent a considerable portion of the thermal radiation from reaching shadow mask 7 all the same, a nickel oxide or nickel iron layer 11 is vapour-deposited on the aluminium layer. As a result, the radiation of the thermal energy evolved in the layers 11 and 12 is effected substantially in a direction away from shadow mask 7. the layers 11 and 12 are so thin and their mechanical contact with the shadow mask is so weak that their deformation does not affect shadow mask 7; however,

they should be sufficiently thick to absorb impinging electrons to a large extent.

FIG. 3 shows another embodiment of shadow mask 7. On the side facing electron gun 2, shadow mask 7 has an aluminum layer 13 vapour-deposited thereon which is connected to shadow mask 7 only along the circumference of the apertures 8. The space between layer 13 and shadow mask 7 is empty. Such a shadow mask is made as follows. An organic skin, removable by thermal treatment and consisting e.g., of an acrylic resin, is applied to the apertured shadow mask on the side which is to face electron gun 2. This skin also covers the apertures 8. Subsequently, the apertures 8 are blown through by means of air. The skin appears to withdraw also from the inner walls of the edges of the apertues 8. Subsequently, an aluminium layer 13 hav ing a thickness of e.g., 0.5 am is vapour-deposited and adheres to the edges of the apertures 8. Layer 13 has subsequently a graphite layer 14 applied thereto which is sprayed by means ofa graphite suspension and serves to increase the radiation of thermal energy in a direction away from shadow mask 7. After removing the skin by thermal treatment, the shadow mask partially shown in FIG. 3 is obtained.

What is claimed is:

l. A cathode ray tube for displaying coloured pictures comprising, in an evacuated envelope, means for generating a number of electron beams, a display screen comprising a large number of regions luminescing in different colours, and a colour selection electrode having a plurality of apertures, said electron beams being each assigned to luminescent regions of one colour by means of the colour selection electrode which colour selection electrode is provided with a layer for reducing the temperature of the colour selection electrode, characterized in that on the side facing the means for generating the electron beams, the colour selection electrode is provided with an electrically conductive, electron-absorbing layer whose thermal contact with the colour selection electrode is minimal said electron-absorbing layer consisting of a thin metal layer contacting and bonded to the colour selection electrode only along the edges of said apertures.

2. A cathode ray tube as claimed in claim 1, characterized in that said metal is aluminum.

3. A cathode ray tube as claimed in claim 1, characterized in that a porous layer, consisting of individual granules, is sandwiched between the colour selection electrode and the electron-absorbing layer.

4. A cathode ray tube as claimed in claim 1, characterized in that said electron-absorbing layer is a double layer radiating thermal energy well on the side facing the means for generating the electron beams and radiating thermal energy poorly on the other side.

5. A cathode ray tube as claimed in claim 4, characterized in that said double layer consists of an aluminium layer provided with a layer of graphite, nickel oxide or nickel iron on the side facing the means for generating the electron beams. 

1. A cathode ray tube for displaying coloured pictures comprising, in an evacuated envelope, means for generating a number of electron beams, a display screen comprising a large number of regions luminescing in different colours, and a colour selection electrode having a plurality of apertures, said electron beams being each assigned to luminescent regions of one colour by means of the colour selection electrode which colour selection electrode is provided with a layer for reducing the temperature of the colour selection electrode, characterized in that on the side facing the means for generating the electron beams, the colour selection electrode is provided with an electrically conductive, electron-absorbing layer whose thermal contact with the colour selection electrode is minimal said electron-absorbing layer consisting of a thin metal layer contacting and bonded to the colour selection electrode only along the edges of said apertures.
 1. A cathode ray tube for displaying coloured pictures comprising, in an evacuated envelope, means for generating a number of electron beams, a display screen comprising a large number of regions luminescing in different colours, and a colour selection electrode having a plurality of apertures, said electron beams being each assigned to luminescent regions of one colour by means of the colour selection electrode which colour selection electrode is provided with a layer for reducing the temperature of the colour selection electrode, characterized in that on the side facing the means for generating the electron beams, the colour selection electrode is provided with an electrically conductive, electron-absorbing layer whose thermal contact with the colour selection electrode is minimal said electron-absorbing layer consisting of a thin metal layer contacting and bonded to the colour selection electrode only along the edges of said apertures.
 2. A cathode ray tube as claimed in claim 1, characterized in that said metal is aluminum.
 3. A cathode ray tube as claimed in claim 1, characterized in that a porous layer, consisting of individual granules, is sandwiched between the colour selection electrode and the electron-absorbing layer.
 4. A cathode ray tube as claimed in claim 1, characterized in that said electron-absorbing layer is a double layer radiating thermal energy well on the side facing the means for generating the electron beams and radiating thermal energy poorly on the other side. 